Efficient Removal of Elemental Mercury from Coal-Fired Flue Gas over Sulfur-Containing Sorbent at Low Temperatures

Abstract

In the work, sulfur-containing sorbents were employed to remove elemental mercury (Hg0) from coal-fired flue gas. The work used the thermogravimetric analysis, Brunauer-Emmett-Teller method, scanning electron microscopy with energy-dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy to characterize the physicochemical properties of the sorbents. The Hg0 removal performance of these used sorbents from the simulated coal-fired flue gas was evaluated by a bench-scale fixed-bed reactor. The results indicated that a generous amount of elemental sulfur covered the surface and pore structure of the used sorbent. With the rise of H2S selective oxidation temperature, both the sulfur content and specific surface area decreased rapidly. Used-Fe/SC120 could achieve the mercury removal efficiency of above 90% at 90 °C. The high temperature was not conducive to the mercury capture due to the release of surface elemental sulfur. The presence of O2 and SO2 inhibited Hg0 removal in different degrees because of the decreased active sulfur sites and competitive adsorption. Meanwhile, NO promoted the Hg0 removal efficiency by enhancing the Hg0 oxidation. The further analysis showed that the surface elemental sulfur was vital to capture the Hg0 from coal-fired flue gas, which reacted with Hg0 to form HgS.